1. Field of the Invention
The present invention relates to communication systems, and, in particular, to equipment for testing components of hybrid fiber/coax (HFC) communication systems.
2. Description of the Related Art
A network interface unit (NIU) is a component of a hybrid fiber/coax communication system that converts radio frequency signals over a coax cable into telephony and video signals. In an HFC communication system, communication signals are conveyed between a central office (CO) and an array of NIUs over a combination of linear lightwave networks (e.g., over optical fibers) and coaxial cable networks. The CO contains a host digital terminal (HDT) and other communications equipment, such as video amplifiers, receivers, and transmitters. Communication signals originating from sources (e.g., interoffice networks, cable-access television (CATV), video, and other broadband services) external to the CO are sent to the HDT and the other equipment at the CO. These signals are formatted and transmitted to the NIUs by the HDT and the other equipment at the CO in accordance with a communication protocol and format being followed by the HFC communication system.
The NIUs are electrically connected to and communicate with customer premises equipment (CPE). CPE may include such devices as telephones, computers, television receivers, and other communication equipment. The NIUs process the messages and communication signals from the CO, format the signals, and transmit the signals to the proper customer equipment. The NIUs also transmit responses to the HDT as well as unsolicited messages (e.g., off-hook indication) in accordance with the system protocol. Most of the communication signals and all of the messages received by the NIUs are transmitted by the HDT. In addition to transmitting communication signals to NIUs throughout the network, the HDT also receives messages from the NIUs. The HDT must be able to identify the type of the received signal, associate that signal with a particular NIU, transfer the received communication signal to the proper external network or service, and, if necessary, properly respond to the particular NIU that sent the signal. The HDT must also be able to detect new NIUs that have been added to the communication system and assign identification numbers to these NIUs.
In designing and testing such an HFC communication system, it becomes very impractical to test the proper functioning of the HDT and the communication between the HDT and the NIUs in an HFC communication system that contains a relatively large amount of NIUs. That is, in order to test an HDT's ability to communicate randomly with any of the NIUs at any particular time, an actual HFC communication system containing all required NIUs could be constructed. This would not only be costly and time consuming, it would severely retard the design and development of such communication systems.